Gate circuit for electric organ



Aug. l2, 1958 c. L. woLGAsT GATE CIRCUIT FOR ELECTRIC oRGAN Filed June 30. 1953 0 E 7. @F3 f 6 Mm ,1 W 4 k M r www W www w f f /H wf me 4 @i 4. Mg .am /w` zo i fw J M i..fzl 21,.; w/m f @m 45H 6 i l J m WL v United Statesy Patent O GATE CIRCUIT FOR ELECTRIC ORGAN Carl L. Wolgast, Niagara Falls, N. Y., assiguor to The Rudolph Wurlitzer Company, North Tonawanda, N. Y., a corporation of Ohio Application .lune 30, 1953, Serial No. 365,183

4 Claims. (Cl. 841.04)

This invention is concerned generally with an electronic organ, and more particularly with a gate circuit for controlling the amplification of an organ amplifier according to whether or not a musical note is generated.

Most electronic amplifiers tend to pick up some hum in the early stages of the amplifier. This hum is amplified by succeeding stages and may be of significant magnitude at the output stage. More specifically, in an electronic organ of the electrostatic type, the generator voltages are low and high amplification consequently is necessary, thus boosting the hum in the output to a high level. This problem is particularly acute in an electronic organ of the continuous reed type.

The use of a vibratile metallic reed and an associated pickup element as a variable capacitor to generate electrical oscillations resembling organ tones is well known in the art. A reed generator of this type is disclosed in Hoschkc Patent No. 2,015,016. Generation of the notes can be controlled by applying a potential continuously across each reed and its associated pickup, and by blowing air past a reed to cause it to vibrate when it is desired to play the corresponding note. Generation also can be controlled by continuously blowing air past all of the reeds in an organ to vibrate the reeds continuously, and by applying potential across a reed and associated pickup when it is desired to play the corresponding note. The latter type of generation control has certain advantages in that there is no time lag due to inertia of the reed which slows starting and stopping, and in that a more economical organ can be fabricated. This type of organ is known as a continuous reed organ.

When air is blown continuously past a vibratile reed and associated pickup, the friction of the moving air develops a static charge between the reed and pickup. Thus, even when no potential is applied across a reed and pickup, there is a tendency to generate a note. This tendency appears as a number of relatively low volume spurious notes in the koutput of the organ translated into audible sound by a loudspeaker in the organ. When one or more organ notes are being played, they are of suliiciently higher volume than the spurious notes to mask or cover the spurious notes so that the latter are not heard at all. However, when no note is being played the combination of all of the spurious notes and of hum picked up in earlier stages of the amplifier produces a most annoying audible hum from the organ loudspeaker.

The general object of this invention is to correct the situation outlined above.

Another object of this invention is to provide, in an 2,846,914 Patented Aug. 12, 1958 ice Other and further objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawing, wherein:

Fig. l is a block diagram of a portion of an electronic organ circuit embodying the principles of the invention;

Fig. 2 is a schematic wiring diagram of the gate circuit or volume reducing stage; and

Fig. 3 is a perspective View illustrating the keying of the gate circuit.

Referring now in greater particularity to the figures wherein like numerals are used to identify similar parts throughout, there will be seen in Fig. l a plurality of continuously operable reeds acting as organ tone generators indicated generally at 8 and connected to a gate circuit 10 through a suitable preamplifier stage or stages (not shown). The amplification of the gate circuit is determined by a plurality of parallel connected gate switches indicated generally at 12. The output from the gate circuit 10 is applied to a phase inverter 14 or other push-pull driving device such as a transformer. The phase inverter 14 in turn drives a pair of push-pull connected output tubes 16 which are conventionally connected to an output transformer 18, the output of the transformer beingtranslated into audible sound by a speaker 20, A feed-back circuit 22 preferably is connected from the output transformer back to the gate circuit for improved linearity and further elimination of hum.

The gate circuit 10 is illustrated more fully in Fig. 2, wherein the input may be seen to be connected through a capacitor 24 in series with a resistor 26 to the control grid or element 28 of an electron tube 30 or an equivalent electronic valve. The tube 30 is provided with a plate 32 which is connected through a load resistor 34 to a B+ source. The output from the gate circuit l0 is provided by means of a capacitor 36 connected to the plate 32.

The tube 30 is provided with a cathode 38 which is grounded through series connected resistors 40 and 42, the former of which may be by-passed by a capacitor 44. The feed-back circuit 22 is connected to the junction between the resistors 40 and 42 as indicated by the arrow at FB. The cathode further is connected through a resistor 46 to a B+ source, this latter B-lsource being grounded through a voltage divider comprising series connected resistors 48 and 50, the latter being grounded as at 52,

The junction between the resistors 43 and 50 is connected by wires 54 to the gate switches 12 indicated in Fig. 2. The gate switches 12 are connected through a resistor 56 to a filter 60, and this filter is in turn connected through a resistor 62 to the grid 28, a grid resistor 64 being provided according to conventional electronic circuity. The junction between the resistor 56 and lter 60 is connected t-o ground through a capacitor 53.

The values 'of the circuit elements are chosen so that with the gate switches 12 open, the gain of the gate circuit stage is one. When one or more of the gate circuit switches 12 are closed, potential is applied through the wires 54, the switches 12, resistor 56, filter 60 and resistor 62 to vary the bias upon the grid of the tube 3f) and thereby to raise the amplification factor to ten. reducing the amplification factor to one, rather than by cutting off the tube 30 completely, clicks caused by opening and closing of the switches 12 are avoided. The filter 60 is of any suitable construction to cause the amplification factor to build up and decay similarly to the build up and decay of musical notes generated by the organ. This insures that all portions of the musical notes will be passed without having the amplification unnecessarily high to pass portions of the hum or spurious notes gen- 3 erated. The filter 58 also keeps the amplification from dropping rapidly at the end of a note in yorder that successive notes when played in rapid sequence all will be amplified identically without any build up or decay of the grid bias at the tube and consequently bias at the tube 30 and consequently of the amplification-of the gate circuit 10.

One key 66 of an organ keyboard is shown in Fig. 3. This key may be lof any suitable construction and is flexibly mounted by means of a metallic bar 68 and a leaf spring 70 on a xed support (not shown). A plurality of exible wires 72 is mounted on a xed insulating member 74 beneath the key 66 and bar 68. The wires 72 pass through suitable apertures in an insulating strip 76 which is mounted by suitable means (not shown) for vertical reciprocation. A bumper or abutment member 78 on top of the strip 76 is engageable by an actuating member 80 carried by the bar 68 to deflect the wires 72 downwardly when the key 66 is depressed.

It will be understood that there is a plurality of keys similar to the key 66 and that there are a set of flexible wires and associated parts for each key, the keys being laterally spaced in a conventional keyboard. This arrangement is illustrated in part by a key bar 68a and mounting spring 70a, a set `of flexible wires 72a mounted on an insulating support 74a, and a bumper 78a engageable by an actuator 80a.

A plurality of insulating rods 82 made of suitable material such as Bakelite is mounted in suitable supports such as the support 84. The rods are mounted transversely of the keys and there is one rod for each wire of a set of wires 72. The wires 72 are adapted to engage the rods 82 when the wires are deected downwardly. All of the rods except for the bottom one are rotatably mounted and carry longitudinally extending conductive inserts, the rods being rotatable by suitable stop controls selectively to position each insulating rod or its conductive insert for engagement lby corresponding wires of the several sets. Thus, whenever a key is depressed a potential is applied to whichever of the wires 72 engages a conductive insert in a rod 82, thereby to energize tone generating reeds according to the note played and according to the stop chosen.

The bottom rod, identified by the numeral 86, either may be a conductive member or may be insulating and carry a conductive member permanently positioned for engagement by all of the lower wires, specifically identitied by the numeral 88. The rod 86 and Wires 88 form the gate switches 12. It will be understood that the rod 86 and wires 88 are repeated for each keyboard in the organ, and that all lof the rods 86 are electrically connected in parallel and all of the wires 88 are electrically connected in parallel.

Accordingly, whenever any key is depressed to play a note, one of the gate switches 12 is closed to change the bias on the grid of the tube 30 and thereby to raise the amplification from one to ten to amplify the musical note. The unitary amplification with the organ in idle condition, but turned on, prevents hum and spurious notes from being amplified to a point where they are audible in the output of the organ. The unitary amplification, as opposed to complete cutting off of the gate circuit, avoids key clicks that otherwise would be present whenever one of the gate switches 12 was opened or closed.

The specific example herein shown and described is illustrative only and is not to be construed as a limitation on the invention. Various changes in structure can be made and form a part of the invention in so far as they fall within the spirit and scope of the appended claims.

The invention is hereby claimed as follows:

l. In a continuous reed electronic organ, the gate circuit comprising an electronic tube having plate, grid, and cathode elements, an input circuit connected to the grid and cathode elements of said tube, a plurality of continuously vibrating wind driven organtone generator reeds tending to accumulate static charges, a plurality of organ keys individually manually movable from idle to playing position operatively to connect said tone generators selectively to said input circuit, a source of B+ voltage, a voltage divider connected to said source of B+ voltage and to said cathode element normally to limit amplification of said tube to a low value with all of said keys in idle position, and means including voltage divider means for applying B+ voltage to said grid element when a key is moved to playing position to raise the bias of said grid element relative to said cathode element to effect substantially higher amplification of said tube.

2. In a continuous reed electronic organ, the gate circuite comprising a single electronic tube having plate, grid, and cathode elements, an input'circuit connected to the grid and cathode elements of said tube, a plurality of continuously vibrating organ tone generator reeds, a plurality of organ keys individually manually movable from idle to playing position operatively to connect any number of said tone generators selectively to said input circuit, a source of B+ voltage, a first voltage divider connected to said source of B+ voltage and to said cathode element normally to limit amplification of said tube to a low value but not cut off, a second voltage divider connected to said source of B+ voltage, a filter for controlling attack and decay of amplification by said tube, and means operative upon movement of one of said keys from idle to playing position yto interconnect said second voltage divider, said filter, and said grid element to raise the bias of said grid element relative to said cathode element for effecting a substantially higher level of amplification.

3. In -a continuous reed electronic organ as set forth in claim 1, a plurality of key switches individually operable by said plurality of organ keys, said key switches including a common switch contact and a plurality of indi` vidual contacts individually operable by said keys to contact the common switch contact.

4. In a continuous reed organ as set forth in claim 3, a plurality of common contacts, and a plurality of individual contacts associated with each key and operable thereby to engage said common contacts.

References Cited in the le of this patent UNITED STATES PATENTS 2,266,030 Hammond Dec. 16, 1941 2,357,191 Hanert Aug. 29, 1944 2,480,132 Hammond et al Aug. 30, 1949 2,577,753 Hanert Dec. 11, 1951 2,596,138 Feiner et al May 13, 1952 2,639,639 Schmidt May 26, 1953 

